Abstract. The Weather Research and Forecasting Hydrological
(WRF-Hydro) system is a state-of-the-art numerical model that models the
entire hydrological cycle based on physical principles. As with other
hydrological models, WRF-Hydro parameterizes many physical processes. Hence,
WRF-Hydro needs to be calibrated to optimize its output with respect to
observations for the application region. When applied to a relatively large
domain, both WRF-Hydro simulations and calibrations require intensive
computing resources and are best performed on multimode, multicore
high-performance computing (HPC) systems. Typically, each physics-based
model requires a calibration process that works specifically with that model
and is not transferrable to a different process or model. The parameter
estimation tool (PEST) is a flexible and generic calibration tool that can
be used in principle to calibrate any of these models. In its existing
configuration, however, PEST is not designed to work on the current
generation of massively parallel HPC clusters. To address this issue, we
ported the parallel PEST to HPCs and adapted it to work with WRF-Hydro. The
porting involved writing scripts to modify the workflow for different
workload managers and job schedulers, as well as to connect
the parallel PEST to WRF-Hydro. To test the operational feasibility and the
computational benefits of this first-of-its-kind HPC-enabled parallel PEST,
we developed a case study using a flood in the midwestern United States in
2013. Results on a problem involving the calibration of 22 parameters show that
on the same computing resources used for parallel WRF-Hydro, the HPC-enabled
parallel PEST can speed up the calibration process by a factor of up to 15
compared with commonly used PEST in sequential mode. The speedup factor is
expected to be greater with a larger calibration problem (e.g., more
parameters to be calibrated or a larger size of study area).